The present invention relates to the field of environmental measurement technique for separating and analyzing an injurious material, and particularly to a technique in which a material contained and mixed in water and injurious to a human body is separated and ionized under atmospheric pressure. Then the ions are separated and analyzed on the basis of the mass-to-charge ratio (hereinafter referred to as "mass") by using an electric field to thereby detect the injurious material. The present invention also relates to a mass spectrometer in which a small amount of metal in water is ionized by using plasma and then the ions are separated and analyzed on the basis of the mass-to-charge ratio by using an electric field to thereby detect the small amount of metal.
A mass analyzing method using an ion trap mass analysis region is one of typical methods for separating and analyzing ions on the basis of the mass by using an electric field. Examples of a mass spectrometer provided with an ion trap mass analysis region include a liquid chromatograph/mass spectrometer (LC/MS) for detecting a material contained in water and injurious to a human body; a microwave induced plasma/mass spectrometer (MIP/MS) and an inductive coupled plasma/mass spectrometer (ICP/MS) each for detecting a small amount of metal contained in water, and so on. In these mass spectrometers, large charged droplets, neutral particles, photons, etc. free from the influence of the electric field or magnetic field become causes of noise so that the efficiency of detecting ions to be measured is lowered if they reach the ion detection region. As a conventional technique to reduce noise caused by those other particles (such as large charged droplets, neutral particles, photons, etc.), a method is employed in which a deflector for deflecting the orbit of ions by an electric field or magnetic field is provided before the ions are inputted into the mass analysis region or after the ions are outputted from the mass analysis region so that only the ions are made to reach the ion detection portion selectively. This is because the other particles are not influenced by the deflector so that the other particles go on an orbit different from the orbit of the ions so as not to reach the ion detection region.
An ion deflector of high performance is required for deflecting ions as described above. An example of the ion deflector provided in the front of the mass analysis region is disclosed in JP-A-7-85834, and an example of the ion deflector provided in the rear of the mass analysis region is disclosed in JP-A-61-107650.
One typical configuration of the LC/MS in which an ion deflector using an electric field is provided in the front of the mass analysis region is shown in FIG. 10.
A sample is delivered to an ion source 1 from means for separating a mixture in a solution, such as a liquid chromatograph, or the like. Ions concerning the sample and generated in the ion source 1 are delivered, through an ion introduction small hole 2 opened in a first electrode, to an intermediate pressure region 4 surrounded by first and second electrodes and evacuated by a pumping portion 3 and are further introduced into a vacuum region through an ion introduction small hole 5 opened in the second electrode. In order to prevent so-called clustering in which water molecules are stuck to ions by cooling in adiabatic expansion at the time of introduction of the atmosphere or ions into a vacuum, the first and second electrodes are heated to about 100.degree. C. by a heater. The ions introduced into the vacuum region are accelerated by an extract electrode 6 and delivered to a double cylindrical electrode electrostatic lens 7 which is an ion deflector. The double cylindrical electrode electrostatic lens is constituted by an inner cylindrical electrode 8 and an outer cylindrical electrode 9 which are coaxial with each other. A plurality of opening portions 10 are provided in the inner electrode 8. The electric field of the outer electrode 9 penetrates into the inside of the inner electrode 10 through the opening portions 10, so that a potential distribution for changing the orbit of ions is formed. When the center axis of the ion introduction small holes 2 and 5 and the extract electrode 6 and the center axis of the double cylindrical electrode electrostatic lens are made off, the ions are deflected so as to go on an orbit 11 indicated by a solid line. If an electrode 13 having an opening portion 12 and a mass analysis region 14 having the same center axis as the axis of the opening portion 12 are disposed so that the axis of the opening portion 12 is located on the orbit 11 of ions at a tail end of the electrostatic lens 7, other particles (large charged droplets, neutral particles, photons, etc. free from the influence of the electric field or magnetic field) go on substantially straight orbit 15. Accordingly, because the other particles strike on positions other than the opening portion so that the other particles are prevented from entering the mass analysis region 14, only the ions are taken into the mass analysis region 14 through the ion inlet hole 12. In this occasion, it is preferable that the electrode 13 is heated by a heater, or the like, in order to reduce stain of the electrode 13 with the other particles. In the inside of the mass analysis region 14, the ions are influenced by high-frequency electric field so that the ions are converged to an orbit in accordance with the mass thereof. A buffer gas necessary for stabilizing the orbit of ions is introduced into the mass analysis region 14 from a buffer gas introduction portion 17. The ions are mass-separated by high-frequency electric field in the inside of the mass analysis region 14 and detected by an ion detector 16.
Next, one typical configuration of the LC/MS in which an ion deflector using a magnetic field is provided in the rear of the mass analysis region is shown in FIG. 11.
A sample is delivered to an ion source 1 from meas for separating a mixture in a solution, such as a liquid chromatograph, or the like. Ions concerning the sample and generated in the ion source 1 are delivered, through an ion introduction small hole 2 opened in a first electrode, to an intermediate pressure region 4 surrounded by first and second electrodes and evacuated by a pumping portion 3 and are further introduced into a vacuum region through an ion introduction small hole 5 opened in the second electrode. In order to prevent so-called clustering in which water molecules are stuck to ions by cooling in adiabatic expansion at the time of introduction of the atmosphere or ions into a vacuum, the first and second electrodes are heated to about 100.degree. C. by a heater. The ions introduced into the vacuum region are accelerated by an extract electrode 6 and delivered to a mass analysis region 14. In the inside of the mass analysis region 14, the ions are influenced by a high-frequency electric field so that the ions are converged to an orbit in accordance with the mass thereof. A buffer gas necessary for stabilizing the orbit of ions is introduced into the mass analysis region 14 from a buffer gas introduction portion 17. The ions are mass-separated by high-frequency electric field in the inside of the mass analysis region 14 and then, together with other particles, outputted from the mass analysis region 14.
A pair of sector electromagnets 18 which are provided so as to be opposite to each other and which serve as an ion deflector, are disposed in the rear of the mass analysis region 14. The other particles delivered to the sector electromagnets 18 go on a substantially straight straight-line orbit 19 so as not to reach an ion detection portion 16 because the other particles are not influenced by the magnetic field, whereas the ions delivered to the sector electromagnets 18 are influenced by the magnetic field to go on a circular orbit 20 so as to reach the ion detection portion 16 where the ions are detected.
The ion deflectors in the aforementioned conventional technique are constituted by a double cylindrical electrode electrostatic lens and a pair of sector electromagnets which are disposed so as to be opposite to each other. By using these deflectors, ions and other particles are separated from each other so that noise can be reduced. The following problems, however, arise.
First, the number of assembling steps for producing these deflectors and assembling the deflectors in the apparatus is increased. Furthermore, high assembling accuracy is required. Next, a space for disposing the deflectors is required, so that the scale of the apparatus is increased. With the increase of the scale, a more severe requirement for making evacuation to keep the vacuum is given to a vacuum pump. Furthermore, the cost and the electric power consumed at the time of the operation of the apparatus are increased because of the additional provision of an electric source for the deflectors, the increase of the discharge volume of the pump, and so on. In addition, the number of apparatus parameters for controlling the orbit of ions accurately is increased, so that operating property is lowered.